The firm’s average fund outperformed its peers by 35% over the five years to 31 December 2015, ratings agency FundCalibre found.

Five groups – Unicorn, Stewart Investors, T Rowe Price, Rathbones and SVM – had every qualifying fund outperform over the five year period.

Unicorn’s average fund performances was 50% higher than the index’s bottom group, NFU Mutual, which delivered an average underperformance of 14%.

Second-place Stewart Investors recorded an average outperformance of 28%. Old Mutual Global Investors, T Rowe price and River & Mercantile completed the top five, with outperformance of 23%, 20% and 19% respectively.

The FundCalibre research analyses the majority of actively managed equity funds recognised by the Investment Association and compares them with their sector averages over a five year time frame.

Each fund group’s funds are then collected together to calculate the group’s average fund performance. Fund groups must have a minimum of four qualifying funds to be included in the index.

The findings suggest fund managers that focus exclusively on active fund management do best, while retail banks perform worst (e.g. Halifax, HSBC and Santander) with most in the bottom quartile of the index.

The biggest improver in the ranking from last year was Aviva, which jumped 25 places from 49th to 24th place, with 86% of its funds beating their peers over the past five years.

JO Hambro Capital Management was the biggest faller, down 18 places from 5th to 23rd, despite still having an “extremely strong” five-year track record with the average fund beating the market by 7% and 89% of funds outperforming.

FundCalibre said growth fund groups (e.g. Baillie Gifford, AXA Framlington) and small-cap specialists (e.g. Unicorn, Marlborough) have performed well over the past five years, helped by a strong rally in global equities and growth stocks. Value funds and groups with a value bias (e.g. M&G Investments, Aberdeen Asset Management) have struggled.

Darius McDermott, managing director of FundCalibre, said: “The goal of the index is to highlight to investors those fund houses that are consistently the best stock-pickers and able to repeat their excellence in equity fund management. This consistency is underlined by the fact that nine out of last year’s top ten groups went on to outperform over the following 12 months by an average of 3.5%.”